Furnace



Aug- 29, 1933- c.`E. FOSTER ET AL 1,924,920

FURNACE Filed July '7, 1932 y 2 Sheets-Sheet l uymmumm.'

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Patented Aug. 29, 1933 UNITED STATES PATENT CFFICE shire, and John Edward Oram,

London, England Holloway,

Application .July 7, 1932, Serial No. 621,164, and in Great Britain September 8, 1931 1o claims.

This invention relates to furnaces and particularly electric furnaces of that general character where the air within the furnace is subject to forced circulation over an electric heater as, for example, by means of a fan.

The object of the invention is to provide means,

for facilitating the regulation of the furnace temperature, and for accurately determining when the charge has reached the desired temperature.

When a quantity or a succession of pieces of material have to be heated as rapidly as may be to a particular temperature it has been customary in the past to maintain the furnace at that temperature and then to insert the pieces of material, singly if they are large, or several at a time if they are small, and to leave them in the furnace untilit is assumed on the basis of past experience, that the pieces under treatment have attained the furnace temperature. There has always been an element of doubt in such a process. Usually an exploring experiment has been made by embedding such a device as a thermo-couple in or adjacent to the pieces of material under treatment and to observe the temperature in comparison with the temperature of the furnace as measured by a similar device.

Given material of regular size and heat capacity, the time taken for these two temperature measurements to approximate is then made the standard time for what is known as soaking. It will readily be understood that if there is any change in the number or the size of pieces put in at one time or in the freedom of heat supply to the furnace this arbitrary soaking time may either be insufficient or, on the other hand, may be wasteful because the furnace has to be run longer for a given charge than is really necessary.

In routine manufacturing operations it is not usually feasible to embed a thermo-couple in the charge or collection of material under treatment in the manner described above and until the development, with which this present invention is connected, made available improved methods the arbitrary soaking time had to be accepted.

The soaking time will obviously be reduced and the heating will be more uniform as between different pieces of material if the transfer of heat from the source of heat to the material under treatment is only a very little effected by radiation and is mainly dependent upon forced convection. Such arrangements have been proposed and used wherein the heat is developed in a separate chamber, for instance, an outer annular chamber, and then there is a forced circulation of the air or other gases in the furnace, for instance by (Cl. 26S-5) means of a fan. The more effective this forced convection or circulation the more rapidly will the charge acquire the furnace temperature and the more quickly will the heating be uniform.

All the foregoing considerations are well known and the present invention has for its object the provision of simple means of knowing when the temperature of the charge has approximated closely to that of the furnace and in providing means for automatic temperature regulation in connection therewith. Electric heating lends itself most favourably to such a system of an outer annular heating chamber and a forced convection, for instance, by means of a fan.-

In such a furnace, for instance, electrically heated, the circulating air receives heat in the outer annular heating chamber and gives up heat to the material or charge under treatment,

parting with it by actual gaseous Contact in,

through and around the charge. It will therefore be clear that any differences in temperature of the air before reaching and after passing through the charge will indicate that the charge has not yet reached the temperature of the furnace. It is true that, when a cold charge is first inserted, the air in the process of its rapid circulation will lose so much heat to the charge that it cannot entirely regain-its temperature in the next contact with the heating elements in the outer heating`chamber but this effect is secondary and evanescent and very soon the temperature of the air before reaching the charge will return to its previous steady figure but there will still be a lower temperature in the air which has passed through or around the charge. These temperature differences will become less and less as the charge gets nearer to the desired temperature and ultimately the two gures will be practically tually constant figure. Coupled with this auto-- matic control it is desirable that the operator in charge of the furnace may have an easy visual indication of how the heating is progressing and how soon it is probable that the charge will'be ready to withdraw. This can be most conveniently done in accordance with this invention by means of an autographic recorder making two contemporaneous records, one of the temperature before and the other of the temperature after the charge. The slope of the line recording the temperature after the charge enables the furnace operator to `judge how soon the charge will be ready for withdrawal.

The present invention comprises a heating or cooling apparatus comprising a closed circuit of circulation passing successively over or through a source of heating or cooling and then over or through the material under treatment, wherein is provided means of measuring the temperature of the air, gas or fluid in the closed circuit of circulation after it has been heated or cooled but before it reaches the material under treatment and a second means of measuring the temperature of the air, gas or fluid after it has passed through or around the material under treatment combined with apparatus making separate but contemporaneous records of these two temperatures on a suitable scale or chart so that the approximation of these two temperatures may be indicated and/or recorded.

A further object of the'invention is to provide means for the automatic regulation of the furnace temperature and the indication or recording of the temperature of the charge within the furnace.

In the preferred construction of the apparatus the thermo-couple or resistance thermometer subject to the temperature of the air leaving the charge operates recording apparatus which indicates by a record line indicating constant temperature that the whole of the charge has reached the desired temperature. Also both thermocouples or resistance thermometers may be arranged to operate recording apparatus having a common chart, so that when the two lines marked thereon contemporaneouslyy are substantially coincident, they will indicate that the whole of the charge has reached the desired temperature.

In a modification of the apparatus the two thermo-couples or resistance thermometers are coupled together in opposition so as to give a differential reading on the chart.

The thermo-couple or resistance thermometer in the heated air or other gas or fluid passing to the charge may be arranged to operate furnace temperature controlling apparatus.

The furnace may be generally of the kind set forth in specification forming a part of the application for Letters Patent in Great Britain designated as No. 334,621 having a fan arranged in its lower portion to circulate the air in a closed circuit over or through electric heaters in a space between the insulated walls of the furnace and a receptacle containing the charge, and then over or through the receptacle to the fan.

The indicating or recording apparatus may be of the moving coil type operating a marker or pointer over a moving chart, and when used with two thermo-couples or resistance thermometers is provided with a commutator or like device whereby the circuit f either thermo-couple or resistance thermometer can be placed in series with the moving coil of the marker or pointer as desired, or by a motor intermittently.

The 'furnace recording apparatus may be provided with heating control apparatus and with a motor-operated commutator, so arranged that the recorder and the heat controlling apparatus can be automatically alternately brought into operation periodically.

A manner of carrying out the invention is illustrated by the accompanying drawings wherein Figure 1 is a sectional elevation of the furnace,

Figure 2 a sectional plan through 2-2 of Figure 1 and Figure 3 a'diagram illustrating the complete electrical system when using recording apparatus.

In these drawings a, a1 are the walls and cover of the furnace, which are made of any suitable heat-insulating material, b is an inner or charge receptacle of thin material provided at its upper end with perforations b1 and in its base with perforations vb2 while the extension of its sides below the base is provided 'with perforations b3.

Between the charge receptacle b andthe walls a are arranged a number of electric heaters c. The spaces containing the heaters c form a passage through which air is circulated by ka fan d 'mounted on a shaft d1 passing through the centre of the bottom wall of the furnace to an electric motor e. In the closed circulation of the air as indicated by the arrows, the air passes from the heaters c through the perforations b1 in the charge receiving receptacle b and after passing over the charge in b passes through perforations b2 inthe base of b to the fan d which drives it through the perforationsb back to the heaters c. The charge receiving receptacle is supported in the furnace on supporting members h, h.

In the furnace a thermo-couple or resistance thermometer t1 is arranged in the heated air passing through the perforations b1 on to the charge in the receptacle b, and a similar thermocouple or resistance thermometer t2 is arranged between the fan d and the perforations b2 in the base of the charge receptacle b, see Figures l and 2.

The connection of the thermo-couples t1 and t2 to an indicating and recording instrument lc` is indicated diagrammatically by Figure 3. In this device the thermo-couples t1 and t2 are connected by leads m and n and m1 and nl to a moving coil m c which carries a marker or pointer operating over a moving chart k1 in the known manner.

The automatic control of the current from mains M1, M2 is preferably of the kind having a presser bar p fixed over the path of a contact p1 carried by the pointer or arm of the moving coil m c and adapted to engage either a high temperature contact p31or a low temperature contact p2 in the known manner. The lead p6 from the arm contact pl extends to one terminal of one coil of a transformer T, the other terminal of this coil being connected to two leads p4 and p5 which terminate repectively in the temperature contacts p3 and p2, each lead having a coil operating'the electromagnet of a mercury switch s having one contact connected by a lead s2 to the mainMl, and another contact connected by a lead s1 to a contacter r3 connected to the main M2.

Periodically by clockwork, or electric motor or other suitable means E, the presser bar p is moved by. the cam El and moves the contacter p1 of the arm or pointer p7 of the moving 4coil m c downwards so that according to the position of the arm the high temperature contact p3 or the low temperature contact p2 will be engaged and so operate the furnace heating control.

By means of a commutator m3 the moving coil m c can be brought alternately into circuit with the thermo-couple t1 and t2 and the change overcan be` effected periodically by driving the commutator by the motor E, at the same time the controlling circuit is made or broken, according to which thermo-couple is connected.

By means of the apparatus described in 0peration the temperature of the air entering the charge space of the oven will be maintained constant by the controlling couple as before indicated and when the apparatus has been started up the temperature of the air leaving the charge space of the oven will correspond with the constant temperature and the record on the chart will be a straight line of constant temperature. If a cold charge is put into the oven chamber the temperature of the air leaving the charge space Will fall rapidly and the line of the recording chart will deviate more or less abruptly from the straight line. As the charge reaches the desired temperature, however, the deviation will get less and less until when the charge has reached the desired pre-determined temperature the record on the chart will have again returned to the original line.

By means of our invention it will be seen that a furnace can be employed at its maximum efficiency and with a minimum of skill asI the desired ultimate temperature of the charge can be provided for by means of the controlling couple and the fact that this desired temperature of charge has been reached will be instantly recorded.

This invention has been described with reference to temperature measurement and control by the use of thermo-couples and a recorder of the direct deflection type but it may be alternatively carried into effect by using thermo-couples and a potentiometric recorder, by resistance thermometers with, for instance, an ohmeter or recording Wheatstone bridge or, in fact, by any method of measuring, recording and controlling the temperatures suitable to the temperature range appropriate to the heating process.

Further, it will be obvious that a similar method of applying this invention for heat treatment at relatively high temperatures may employ an inert gas or an active gas in place of air :for circulating the heat. Alternatively, :for lower temperatures the same method may be used with oil or other fluid in place of lthe air. This invention has been described, in the foregoing explanation, with relation to furnaces and similar apparatus, but it may equally be applied to cooling or refrigeration. In such a case the electric heating coils would be replaced by a refrigerating or cooling agent.

In place of a fan, any other convenient means may be employed to circulate the air, gas or fluid,

.for instance, in the case of oil, a positive pump may be used.

Having now particularly described and ascertained the nature of our said invention and in what manner the same is to be performed, we declare that what we claim is:-

. l. Heat interchange apparatus comprising an insulated chamber for the material under treatment, a heat interchanger, a closed fluid circuit passing successively from the heat interchanger to the material under treatment, means for measuring the temperature of the iiuid before it has reached the material under treatment, means for measuring the temperature of the fluid after it has passed from the material under treatment, apparatus for separately indicating each of said temperatures and apparatus controlled thereby for automatically regulating the temperature of the fluid before it has reached the material under treatment.

2. Heat interchange apparatus comprising an insulated chamber for the material'under treat-x ment, a heat interchanger, a closed fluid .circuit passing successively from the heat interchanger to the material under treatment, means for measuring the temperature of the fluid before it has reached the material under treatment, means for measuring the temperature of the fluid after it has passed from the material under treatment and apparatus making separate contemporaneous records of both temperatures on a suitable chart so that the approximation of these two temperatures may be recorded.

3. An electric furnace comprising a charge receiving receptacle, an electric heating element, a closed fluid circuit passing successively from the electric heating element to the material under treatment, a source of supply of electric current for the heating element, means for electrically measuring the temperature of the circulating iiuid before it has reached the material under treatment and means for electrically measuring the temperature of the fluid after it has passed from the material under treatment, a pointer positioned by said temperature measuring means for indicating both temperatures, and means operated by periodic movement of said pointer for controlling the heating element.

4. An electric furnace comprising Aa charge receiving receptacle, an electric heating element, a closed uid circuit passing successively from the heating element to the material under treatment, a source of supply of electric current for said heating element, an electric thermometer for measuring the temperature of the uid before reaching the material under treatment and a second electric thermometer for measuring the temperature of the iuid after it has left the material under treatment, a moving coil recording apparatus for operating a marker over a moving chart and a commutator for selectively connecting each of the electric thermometers in series with the moving coil of the recording apparatus.

5. `An electric furnace comprising a charge re- 'ceiving receptacle, an electric heating element, a

heating element, an electric thermometer for measuring the temperature of the uid.. before reaching the material under treatment and a second electric thermometer for measuring the temperature of the uid after it has left the material under treatment, a moving coil recording apparatus for operating a marker over a moving chart, a commutator and an electric motor driving said commutator for alternately connecting each of the electric thermometers in series with the moving coil of the recording apparatus.

`6. An electric furnace comprising a charge receiving receptacle, an electric heating element, a closed uid circuit passing successively from the heating element to the material under treatment, a source of supply of electric current for said heating element, an electric thermometer for measuring the temperature of the fluid before reaching the material under treatment and a cording to which of the electric thermometers is connected.

"1. A heat interchange apparatus comprising a charge receiving receptacle, a heat interchanger, means for circulating a uid through the interchanger and the receptacle in a closed circuit, a thermometer subjected to changes in temperature of the uid before it enters the receptacle, a separate thermometer subjected to changes in the temperature of the fluid after it leavesthe receptacle, a travelling chart, a single marking nger, and thermostatic mechanism operating the single nger from each thermometer separately to produce separate markings on the chart which coincide when the temperature of both thermometers is the same.

8. A heat interchange apparatus comprising a charge receiving receptacle, a. heat interchanger, means for circulating a uid through the interchanger and the receptacle in a closed circuit, a pyrometer subjected to changes in the tempera- Ature of the iiuid before it enters the receptacle, a

separate pyrometer subjected to changes in the temperature of the fluid after it `leaves the receptacle, a travelling chart, a clock driven commutator, a single marking linger operated electromagnetically by a floating coil, mechanism for bringing the marking finger into contact with the chart periodically, each pyrometer being brought into circuit with the coil of the marking linger alternatively by the commutator, and the mechanism for bringing the pointer into contact with the chart periodically being operated from the clock driven commutator.

9. A heat interchange apparatus comprising a charge receiving receptacle, a heat interchanger,

means for circulating a fluid through the interchanger and the receptacle in a closed circuit, a thermometer subjected to changes in temperature of the fluid before it enters the receptacle, a separate thermometer subjected to changes in temperature of the uid after it leaves the receptacle, a thermostatic temperature regulator, and a temperature indicator, and means for intermittently connecting either the regulator or the indicator and simultaneously disconnecting the other to and from one of the thermometers.

10. A heat interchange apparatus comprising a charge receiving receptacle, a heat interchanger, means for circulating a fluid through the interchanger and the receptacle in a closed circuit, a pyrometer subjected to changes in the temperature of the fluid before it enters the receptacle, a separate pyrometer subjected to changes in temperature of the fluid after it leaves the receptacle, a thermostatic temperature regulator, a travelling chart, a clock driven commutator, a single marking ringer operated electromagnetically by a floating coil, mechanism operated by the commutator for bringing the marking finger into contact with the chart periodically, the contacts on the commutator having separate connections to each pyrometer and the temperature regulator, and operating during the rotation of the commutator to intermittently connect either the regulator or the coil of the marking nger to one of the pyrometers while simultaneously disconnecting the other.

CHARLES EDWIN FOSTER. JOHN EDWARD ORAM. 

